Jeremy Hunt, the Health Secretary, will back amendments to the Children and Families Bill to create a new “age of sale requirement” for e-cigarettes and make “proxy” purchasing – knowingly buying tobacco on behalf of someone under 18 - illegal.

E-cigarettes have become increasingly popular among adults who are trying to give up smoking. Some 1.3 million people in Britain are believed to have switched from smoking conventional cigarettes to the electronic vaporising devices.

E-cigarettes give the smoker a hit of nicotine, a highly addictive drug, and are widely thought to be safer than cigarettes.

However, Professor Dame Sally Davies, the government’s chief medical officer, said: “We do not yet know the harm that e-cigarettes can cause to adults let alone to children, but we do know they are not risk free.

“E-cigarettes can produce toxic chemicals and the amount of nicotine and other chemical constituents and contaminants, including vaporised flavourings, varies between products meaning they could be extremely damaging to young people’s health.”

At present there is no legal restriction on people under the age of 18 buying products like e-cigarettes containing nicotine, which officials say represents a serious legal loophole at a time when e-cigarettes are becoming increasingly popular with teenagers.

Medical professionals are concerned that these products, which give young people a taste for nicotine, could lead to an increase in the number of teenagers smoking.

E-cigarettes consist of a battery, a cartridge containing nicotine, a solution, and an atomiser to turn the solution into vapour.

The nicotine is delivered without a flame and without tobacco or tar and e-cigarette users describe the experience as “vaping” rather than smoking.

In a bid to restrict children’s access to cigarettes further, a new offence will be created which will mean any adult who buys cigarettes or other tobacco products for someone who is under 18 could be given a £50 fixed penalty notice or fined up to £2,500.

Jane Ellison, the Public Health Minister, said: “Two thirds of smokers say they smoked regularly before they were 18, showing that this is an addiction largely taken up in childhood.

“This measure is designed to help protect children from the dangers of being bought cigarettes by irresponsible adults.”